In some cases, to improve the durability of an electrode (e.g., a center electrode or a ground electrode) of a spark plug, a highly durable tip (for example, a tip containing a noble metal) is fixed to the electrode. One technique proposed to fix a ground electrode tip is to weld the tip to a ground electrode by irradiating the interface between the ground electrode and the ground electrode tip with, for example, a laser beam while moving the laser beam. In another proposed technique, the power of the laser beam is gradually reduced in consideration of the fact that heat imparted by the laser beam transfers through a molten portion to cause the temperature of a portion unirradiated with the laser beam to increase. For a prior art example, see Japanese Patent Application Laid-Open (kokai) No. 2012-74271 (“Patent Document 1”).
When the power of the laser beam is reduced, proper welding may not be possible. For example, in some cases, the laser beam becomes unstable, and the irradiation with the laser beam stops unintentionally. This is a common problem not only when the laser beam is used but also when energy beams such as electron beams are used.
The present description discloses a technique for welding a tip appropriately using an energy beam.